System for controlling an oxygen concentration in exhaust gases

Abstract

A system for controlling an oxygen concentration in exhaust gases emitted from a combustion engine. An oxygen sensor which changes a resistance in response to a sensed presence and absence of oxygen in exhaust gases is connected in series with an electric power source and a transistor to produce an output voltage indicative of the sensed presence and absence of oxygen. A comparator compares magnitudes of the sensor output voltage with a predetermined magnitude. In response to an output voltage of the comparator, the transistor controls a biasing current flowing from the electric power source to the sensor so that, when either presence or absence of oxygen is sensed, the sensor output voltage is kept substantially at the predetermined magnitude irrespective of temperature dependent changes in the resistance of the oxygen sensor.

What we claim is: 
     
       1. A system for controlling an oxygen concentration in exhaust gases emitted from a combustion engine comprising: means for sensing a presence and absence of oxygen in exhaust gases emitted from a combustion engine to produce an output signal having magnitudes respectively indicative of said presence and absence of oxygen;   means for comparing said magnitudes of said output signal of said sensing means with a predetermined magnitude indicative of a reference concentration between said presence and absence of oxygen;   means for controlling said oxygen concentration in said exhaust gases toward said reference concentration in response to an output signal of said comparing means; and   means for controlling either one of said magnitudes of said output signal of said sensing means toward another predetermined magnitude in response to said output signal of said sensing means;   wherein said sensing means includes an oxygen responsive titanium dioxide, and wherein said latter controlling means includes:   comparison means for comparing said magnitudes of said output signal of said sensing means with said another predetermined magnitude;   integration means for integrating an output signal of said comparison means; and   biasing means for biasing said sensing means by an electric current in response to an output signal of said integration means.   
     
     
       2. A system according to claim 1, wherein said biasing means includes: a source of electric power; and   a transistor having an emitter-collector path connected in series with said source of electric power and said sensing means and having a base connected to be responsive to the output signal of said integration means.   
     
     
       3. A system for controlling the oxygen concentration in the exhaust gas emitted from a combustion engine comprising: means including titanium dioxide for exhibiting resistance in response to the presence and absence of oxygen in said exhaust gas;   means for supplying said resistance exhibiting means with an electric current to convert said resistance into a voltage signal indicative of the presence and absence of oxygen;   first means for comparing said voltage signal with a first predetermined value indicative of a desired oxygen concentration;   means for controlling the oxygen concentration toward said desired oxygen concentration in response to an output signal of said first comparing means;   second means for comparing said voltage signal with a second predetermined value different from said first predetermined value; and   means for controlling said electric current supplied to said resistance exhibiting means in response to an output signal of said second comparing means to thereby keep said voltage signal indicative of one of the presence and the absence of oxygen at said second predetermined value.   
     
     
       4. An apparatus for controlling the concentration of oxygen in the exhaust of a combustion engine comprising: means responsive to the presence and absence of oxygen in said exhaust and exhibiting an abrupt change in resistance therebetween for sensing the presence and absence of oxygen in said exhaust;   means responsive to an output of said sensing means for minimizing the variation in the concentration of oxygen from a predetermined oxygen concentration level;   means for providing a variable biasing current to said sensing means to obtain a first voltage in response to said abrupt change from a high resistance to a low resistance, relative to one another, said first voltage being indicative of an oxygen concentration varying from said predetermined oxygen concentration in one direction; and to obtain a second voltage in response to said abrupt change from a low resistance to a high resistance, relative to one another, said second voltage being indicative of an oxygen concentration varying from said predetermined oxygen concentration in the other direction; wherein a predetermined one of said first voltage and said second voltage is maintained at an approximately constant level and is substantially insensitive to the slowly changing resistance of said sensing means over a broad range of resistance values;   means for providing a first reference voltage wherein said first voltage is maintained at an approximately constant level equal to the level of said first reference voltage and said second voltage is greater than said first voltage and decreases slowly as a function of time, and wherein said biasing current varying means comprises:   a first comparator responsive to said reference voltage and the voltage across said sensing means;   an integrator responsive to an output of said comparator; and   a current generator responsive to an output of said integrator and connected to said sensing means for providing said biasing current.   
     
     
       5. The apparatus as in claim 4 wherein said current generator comprises a transistor, said transistor having a base thereof connected to the output of said integrator and a collector thereof connected to said sensing means whereby said transistor slowly decreases said biasing current in response to a relatively slowly increasing voltage generated by said integrator when the voltage across said sensing means exceeds said first reference voltage, and quickly increases said biasing current in response to a relatively quickly decreasing voltage generated by said integrator when the voltage across said sensing means is less than said reference voltage, thereby causing said first voltage to vary minutely about the level of said reference voltage in order to maintain said first voltage at an approximately constant level, and causing said second voltage to decrease slowly. 
     
     
       6. The apparatus of claim 5 further comprising means for providing a second reference voltage indicative of said predetermined oxygen concentration level, said second reference voltage being greater than said first reference voltage and less than said second voltage, wherein said variation minimizing means comprises a second comparator responsive to said second reference voltage and the voltage across said sensing means and having the output thereof connected to a mixture supply control device. 
     
     
       7. The apparatus of claim 6 wherein an oxygen responsive portion of said sensing means is titanium dioxide.